Generator drive control system



Aug. 8, 1 950 SPENCER 2,518,394

GENERATOR DRIVE CONTROL SYSTEM Filed Oct. 28, 1948 S TANDEY ALTERNATOR S E T CURRENT L /M/ TING .S' TARTEI? NORMAL arm/v4 70R ssr INVENTOR 8y H.H. SPENCER A T TORNE V Patented Aug. 8,

UNITED STATES PATENT OFFICE GENERATOR DRIVE CONTROL SYSTEM Harry H. Spencer, Springfield, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application October 28, 1948, Serial No. 57,039

14 Claims. I

This invention relates to power supply systems and more particularly to an automatically controlled power plant for uninterruptedly supplying current to a load irrespective of failures or voltage fluctuations in excess of predetermined magnitudes of a primary commercial power supply source from which current is normally supplied to the power plant.

The invention is of use, for example, for supplying energizing current to equipment of a carrier current telephone system, which requires for its continuous operation, an uninterrupted supply of alternating current the voltage of which remains within a predetermined amplitude range.

An object of the invention is to provide improved motor-generator apparatus for supplying current to a load without interruption or exces sive voltage variation, irrespective of interruption or amplitude change of current normally supplied to a driving motor of said apparatus.

In accordance with an embodiment of the invention described herein for the purpose of illustration, an alternator for supplying current to a load has coupled to it an alternating current motor and a direct current motor for driving it. During normal operation, current is supplied from a commercial alternating current source to the alternating current motor causing it to drive the alternator. During a starting period and during periods when the voltage of the alternating current source falls below a certain minimum value, the direct current motor is energized by current from a battery to cause it to drive the alternator. A standby alternator set assumes the supply for the load if the alternator output voltage falls below a certain minimum value while the direct current motor is driving the alternator.

Apparatus is provided for controlling the energization of the two motors and the standby alternator set under joint control of the alternator output voltage and the alternating current supply line voltage. This control apparatus makes possible the transfer of the alternator drive from one motor to the other without introducing large amplitude voltage variations at the alternator output.

When the drive is transferred from the direct current motor to the alternating current motor, the battery remains connected to the direct current motor so that it may more readily assume the drive of the alternator. A resistor is inserted in the armature circuit of the direct current motor to limit the armature current while the alternator is being driven by the alternating current motor, the resistor being short-circuited 2 when the direct current motor drives the alternator.

Apparatus is also provided to prevent hunting between the two motors due to fluctuations either of the commercial power service line voltage or of the alternator output voltage of relatively small amplitude.

Another feature of the invention is means to transfer the drive from the alternating current motor to the direct current motor if the alternator output voltage drops to a certain value below normal. This feature will be of value in the event the commercial power service line voltage remains normal but its frequency decreases so that the alternating current motor is unable to properly maintain the alternator output voltage. If the decrease in the alternator output voltage was due to a failure in the alternator itself, means are provided to shut down the normal motor-generator set and to transfer the load to a similar standby set, but not before the alternator drive is transferred to the direct current motor.

Other objects, features, and aspects of the invention will be understood from the following description made with reference to the single figure of the drawing which shows a simplified circuit schematic of a power plant embodying the features of the invention.

Referring to the drawing, an alternating current load I l is connected to receive power either from a normal two-motor alternator set [0 comprising alternator l2 mechanically coupled to a direct current motor l3 and an alternating current motor l4, or, as shown in the drawing, from a similar standby alternator set 49. The normal supply set In is started initially by manually operating the start switch [5. This operation of contact a of start switch l5 connects the holding battery 16 through the normally closed contact a of stop switch I l to the winding of relay i8, causing it to operate. The operation of relay [8 connects the supply battery [9 to the field winding 20 and control rheostat 2| of motor it in series. The same operation also connects the battery l9 through a conventional current-limiting starter 22 and the closed contact of relay 23 to the armature of the direct current motor 13, bringing it up to normal speed. The winding of relay 23 is energized by the battery l6 with ground established through the upper contact of relay 24.

When the terminal voltage of alternator [2 has reached a certain value as determined by the adjustment of rheostat 25, the current through the transformer 26, rectifier 21, and the winding of relay 28 will cause relay 28 to operate. With relay 24 deenergized, the rheostat 29 is short-circuited by the leads 3!! through the lower contact of relay 24.

The operation of relay 28 removes ground from the winding of relay 3| causing relay M to release. While relay 28 is deenergized, relay 3| is operated by current from a holding'batte'ry 32 flowing in a circuit comprising an armature'and contact of relay 33 and the armature and a contact of relay 28. The relay 33 is normally held operated by current from the commercial supply 36 flowing through transformer '31, rectifier 33, and rheostat 39, and when operated-connects the battery 32 to one terminal of each of'the windings of relays 3! and as. Bheostat 43 is short-circuited by the lead All through the-lower contact-and armature of relay 33.

The ground connection removed fromrelay 3! due to the operation-of relay 28 is now anplied'to-thewinding of "a slow actin relax/ 3 i causing it to operate. Both relays 34 and 35 have on'e side or their'windin'gs connected to the h'o din g battery [6. Relay '35 therefore operates when the o eration ofrelay "s4 'connects ground to its w nding. A holdinz circuit for the winding of relay is is establ shed from the battery tfiithrough 'contaet-a f relay 35 sothatthe'start switch l 'rnaynow be" released. Relay ii l is slow acting allowi g relays! to release before the wi d n or 'relay'w': i is grounded through contact c o relay 35.

:R'elav'T-RE inooerating remo 'res'the ground con nect on throu h-its contact b from the winding of relay-"45, caus ng relay 4'5 torelea e 'whenor if' the start 'switchlii is released. This release o'frelay' li transfers a groundcon ect on from the wind ng 'of' relay !.8- to the winding of relay 4?. 'Both relays l-andAB 'ha've'one side of their winings permanently connected tothehol'di battery Hi and, heretofore, re ay 48 has'been held oneratedto connect'the 'load l l to'the standby alternator set M3. The groundconnection" transfer caused by the'release' of relay 45 causesrelay 28 to "release'an'd relay 4? to operate. Relays Hand 48 maybe mechanically'interlockedto prevent one from operatingbe orethe other releases. The release ofre'laye i and'the'sub sequent onerationof relays! transfers the'connection -of the'loadll from thestandb'y set 49 to the normal set Ill.

The release of relay 3! connects ground through a contact at ofrela'y 35 and 'through the normally'clo ed contact b of thestoo switch I"! to the winding of relay 24, causing it to operate if the voltage of the supply 35 is such as, to mainta nrelayss operated. Thisoperation of relay 24 removes ground'from'the'winding. of relay 2-3 causing-it to release, and it also com. pletesfa circuit from ground through a contact of relay 24, the winding of relay'd I andthebattery' IE to ground, causing-relay 4! to operate. The release of relay 23 removes the short circuit from the armature resistance 42 nand the substantially simultaneous operation of relay 4| connects the alternating current motor M to-the commercial supply 36.

The resistance limits shear-mature current of the direct current motor l3 so that-the =al-terthrough the resistance-42 to the armature of the direct current motor 20. It is now necessary only 'oflrelay 24 causing relay 2 to release. lease of relayZ l removes ground from the wind- 'ing of relay il causing it to release which disconnectsthe alternating current motor i l from thecommercialsupply as, and reconnects ground 'to 'the Winding of relay 23 causing it to operate and againshort-circuit the armature resistance 42. Relays 33, 2d and 23 are very fast acting as compared to relays 34, S5 and [B so that the motor drive is transferred to the direct current motel"- l S before theioutput voltage ofthe alternator decreases suiliciently "to allow the series of-relays 28,3,?3 '5'3Ll1d it to release and disconnect the direct currentmotor 13 from its supply battery" [9.

The release oi relay-tta-also removes the, short circuit=irom the rheostat es, thereby increasing the resistance in the winding of. relay 33. Relay 33 therefore will not reoperateauntil' the voltage of supply 35 returns to .-'-a'Va1ue' ab0Ve that-at Which-relay "33 released, the exactyalue being dependent onthe adjustment of the rheostats A3 and39. Thereoperati'on of relay3.3 replacesthe short circuit'on rheostat =43 and returns :the motor drive to the alternating current: motor E by the operation ofxrelays '24 andtl valid the release of relay23 as hereinbefore described.

Emergency conditions, such as fai-lureof the alternating current motor Hi :or the alternator i2, aresafeguarded by -therelay 28 which is "adjusted to': release at=-an=alternator output voltage belownormal and: determined-by the adjustment of rheostats =25and"29. (Whilethe alternating current motor 'M'wis driving the alternator E12, the shortcircuit' onthe: rheostat 29 is removed by. the operation of relay 1 243., which relay: must operate before the alternatingtcurrentmotor M isconnectedto its supply:36,.) -Should the altern'ator i2 output decrease to this predetermined value; relay 28 will-release,- removing ground from the winding'ofrelay liand applying ground to the winding of relayial. Relay-Bl will operate if tha-supply 35 voltage is normal so that the relay-this operated' a-ndwill lockup to ground through contact-c ef relay 35*and itheclosed switch-44. "Relay M, inoperatingw ill remove ground from -the winding of relay 24, thus causing the motor drive to be transferred to the 'direct current motor 'l31as: hereinbefore. described. The release ofs'relay-z i replaces the short circuit on rheostat 29, thuse raising thecurrent in the-winding of relay 28=so that it'reoperates; and replaces the ground on the winding of rela'y 3. Relay 34,-;as3previously described-is slow acting and does not release during the interval s'relay 28 *is released.

The direct current motor t3 drives thealternatorlZ at normalioutput, ii it is able to doso, and direct current motoroperation continues until the lock upgorr relaytl'is'removed by operating the-switches. The: switch- 44 maybe opera a-ted -locally-or by remote control :means well knowninthe art. This operation willcause relay 3| to release which -wi-ll inturncause'the motor drive to -be again transferred: to the alternating,

current motor M as previously described.

But, if motor l3 on assuming the alternator I2 drive is unable to maintain the alternator l2 output voltage, relay 28 will again release at a voltage now determined by the adjustment of only rheostat 25 since rheostat 29 is short-circuited during direct current motor operation by the release of relay 24. This voltage will be lower than that which caused relay 28 to release during alternating current motor drive since the resistance in series with the winding of relay 28 has been decreased by short-circuiting rheostat 29. This removal of ground from the winding of relay 34 by the release of relay 28 will now allow relay 34 to release. The release of relay 34 causes relay 35 also to release by removing ground from its winding. The release of relay 35 removes the battery It from the starting relay l8 causing it to release and shut down the set by removing the supply battery i9 from the direct current motor I 3. The alternating current motor I4 is disconnected from its supply 36 at the time of the motor drive transfer.

The release of relay 35 causing the alternator set I to shut down also reconnects ground to the winding of relay 45 through contact b of relay 35. Relay 45 will now operate since the one side of its winding is permanently connected to the holding battery I 6. The operation of relay 45 transfers the ground connection through its armature from the winding of relay 41 to the 1 winding of relay 48. As hereinbefore described, relay 41 will release, and, in turn, relay 48 will operate. The release of relay 4'! and operation of relay 48 transfers the load I l connection from the normal alternator set [0 to the standby set 49 running normally at no load. The set 49 then assumes the supply for the load I l.

The alternator set I 0 may be stopped at any time by manually operating the stop switch ll. By this operation of the contact a of stop switch ll, the relay 18 will be released, causing the battery l9 to be disconnected from the direct current motor l3. This operation of the contact b of stop switch I! will disconnect the alternating current motor M from its source 36, if it be so connected, by removing ground from the winding of relay 2 causing it to release. The release of relay 24 removes ground from relay ll causing it to release and open its contacts and thus deenergize the alternating current motor l4. The operation of the contact 0 of the stop switch il connects ground to the winding of relay 45 causing relay 45 to operate and transfer the connection of the load II from the normal set Hi to the standby set 49 as hereinbefore described. A holding circuit for relay 45 will be obtained by the ground connection of contact b of relay 35 when relay 35 releases.

For the purpose of performing tests or maintenance on the alternator set It while it is running, the load may be momentarily transferred to the standby set 49 by holding the start switch I depressed. This connects ground to the winding of relay 45 through the contact b of the start switch causing relay to operate and transfer the load II connection to the standby set 49. The release of the start switch' l5 returns the load ll connection to the normal set it by causing the release of relay 45.

Although the invention has been described as relating to a specific embodiment, many modifications thereof will occur to one skilled in the art without deviating from the spirit of the invention. The invention therefore should not be limited to the embodiment as set forth in detail herein.

What is claimed is:

1. In combination, a generator for supplying alternating current to a load, a direct current motor having a field winding and an armature winding, an alternating current motor, means for mechanically coupling said direct current motor and said alternating current motor to said generator for driving it, a circuit for supplying current from an alternating current supply source to said alternating current motor comprising a first switching means for completing said circuit, means for supplying current from a direct current source to said windings of said direct current motor, a resistor connected in series with said armature winding and said direct current source, a second switching means for completing a short-circuiting current path around said resistor, and means responsive to current from said alternating current supply source for opening said first switching means and for substantially simultaneously closing said second switching means when the voltage of said supply source decreases below a certain minimum value.

2. In combination, a generator for supplying alternating current to a load, a direct current motor, an alternating current motor, means for mechanically coupling said direct current motor and said alternating current motor to said generator for driving it, means for supplying current from a direct current source to said direct current motor, means for supplying current from an alternating current supply source to said alternating current motor, and automatic switching means having two conditionsother condition causing said generator to be driven by said direct current motor.

3. In combination, a generator for supplying current to a load, a direct current motor comprising an armature winding and a field winding, an alternating current motor, means for mechanically coupling said direct current motor and said alternating current motor to said generator for driving it, a circuit for supplying current from an alternating current supply source to said alternating current motor com- 'prising a first switching means for completing said circuit, a circuit for supplying current froma direct current supply source to said direct current motor comprising a resistor in series with said armature winding and said direct current supply source, a second switching means for completing a short-circuiting current path around said resistor, and means responsive jointly to the output voltage of said alternator and to the volt-- age of said alternating current supply source foroperating said first and said second switching means.

4. A combination in accordance with claim 3, said last-named means adapted to operate said switching means to transfer the drive of said generator when it is being driven by said alternating current motor from said alternating current motor to said direct current motor in response to a decrease in the voltage of said alter nating current source below a first value.

predetermined 5. A combination in accordance with'claini e, and voltage responsive. means in combination with saidiast-named' means vto automatically operatesaid switchingmeansto return the drive of-said generatonaf-ter having beentransferred from said -.-alternating 1 current motor *to said direct current motor in response to a decrease inthe voltage of said source, to said alternating current motor in response'to an increase in the voltage of said source beyond a second predetermined value higher than said first value.

-6.5-A combination in accordance with claim 3, saidlastt-named means-adapted to operate said switching means to transfer the drive of said generator when ity is being driven by saidalternating current motor from" said alternating current -motor to said direct current motor in response to a decrease inthe output voltageoi said-generator below a third: predetermined value.

:7. A" combination-in accordance with claim 6 andznon-automatic switching means to return the drive of said generator after having been transferred from. said alternating oiu'rent motor tQ-said direct current motor as a'resu t of a decrease in the output voltage of said generator to said alternating current motor.

-:-8.. A combination inaccordance with claim .5, a standby zgenerator normally running at no load, and athirdswitching means operated in response to a decrease in the output voltage of said generator beyond-a fourth predetermined value lower. than said third value to deenergize saidgdirect. current motor and-sequentially disconnect said loadirom said first generator and connect. said load to be supplied by said standby generator.

.9. In combination, a generator for supplying current to a load, a direct current motor C0111 prisingan armature winding and a field winding, an alternating current motor, means for mechanically coupling said direct current motor and said :alternating current motor to said generatorior driving it, a circuit for supplying current from an alternating current supply source to said alternating current motor comprising a first switching means for completing said circuit, a circuit for supplying current from a direct current supply source to said direct our rent motor comprising a second switching means for completing saidcircuit, a resistor in series with said armature winding, and a'third switch-- ingmeans forcompleting a short-circuiting current path around said resistor, means to control said first and said third switching means to alternatively cause said generator to be driven by said alternating current'motor during periods of normal alternating current supply source voltage and normal generator output voltage, or, to transfer the drive of said generator from said alternating current motor to said direct current motorwli'en either of said last-named voltages falls below certain predetermined values, said 'last named means comprising .a fourth switching means responsive to variations in the voltage of I said alternating current supply beyond certain predetermined values and a fifth switching means responsive to variations in the voltage of said generator output beyond certain predetermined limits, and means under control of'said fifth switching means to control said second switching means to deenergize said direct current motor in response to a decrease in the voltage of said generator output beyond a certain predetermined value while said generator isbeing driven bysaid direct current motor.

1 l0.-A1 combination inaccordancewith claim 9 comprising: a standby generator hermally running' at no'-load,-asixth switching means responsive-to the -deenergization: ofsaid direct current motor tosequentiallydisconnect said load from said firstgenerates-and connect said load to said standby genera-tor.

11. .A combination-in: accordance with claim-9 comprising lock-up means to prevent :the drive of said generator: from beingtransferred from said direct current motor to said alternating ourrent-m-otor-when saiddrive has been'transferredto said-direct current :motor from said alternating current motor by said third switchingrmeans.

.12.. Ina system for supplying alternating currentto a' load, a generator, a direct current motor having a field -winding and an. armature winding,=-a resistor: in serieswith said armature winding, ashort-circuiting path "aroundsai'd resistor, 2 firstsswitching'meansto interrupts-aid path,- a circuit to supply current-to -said"motorwind ings =from a-zdirect curr'ent supply "source, an alternating .currentm'otor; as'ourc'e of alternating current, a second switching'nieans "to comb plete a circuit to suppiyzcurrentto-said alterhating currentInotor'from'sai'd alternating currentsource, means .to mechanically couple said current motor rand said alternating current motor to. saidgen'erator to drive it, means comprising said direct current motor "to start said generator and to cause said generator to supply current to said load, and automatic switching means responsive to the increase output "voltage of said generator to a predetermined value to transfer the drive-of said generator fromsaidalternating current-motor to said direct current motor'bysubstantially simultaneously operating said first "switching means to remove said shortcircuit and said second switch-.- in'g'means' to complete said circuit to supplycun rent .to said alternating current motor.

13. A system' for supplying current to a load.

coin-prising'a generator-,a direct current motor, alternating current motor, means to mechani'cally couple said alternating current motor andsaid direct current motor to said generator to drive the latter, an'alternating current'source and means to energize said alternating current motor from said source,ya direct current source andmeans to energize'said direct current motor from said direct-current source, switching means to control said last two-named means to cause said generator to bedriven by either said direct current motor or'said alternating current motor, a resistance in series withthe armature of said. direct current motor and said direct current source, a short-circuiting path around said resistance, andmean's under control of said switching means to open said short-circuiti'ng path when said generator is being driven by said.

alternating current motor.

14. A system for supplying current to a load comprising a generator, a direct current motor, an alternating current motor, means to mecham ically couple saidalternating current motor and said direct current motor to said generator to drive it, a direct current source and means to energize said direct current motor by said source, an alternating current source, switching means to cause said generator to be drivenby alternating current motor or saidv direct current motor alternatively, means under control of said.

switching meanslto. cause said alternating current motor to be energized by said alternating;

9 current source when said generator is driven by said alternating current motor, a resistance in series with the armature of said direct current motor and said direct current source, a shortcircuiting path around said resistance, and means under control of said switching means to remove said short-circuiting path when said generator is being driven by said alternating current motor.

HARRY H. SPENCER.

REFERENCES CITED UNITED STATES PATENTS Number Name Date Bany Aug. 12, 1941 

